Interferometry-based techniques are used in various applications such as length measurement, as well as inspection of sample, e.g. biological samples. Generally, these techniques are based on the use of a change in an interference pattern of two light beams to determine of a phase shift induced in one of the beams by its interaction with a sample under inspection.
Interferometers can also be used for the measurement of a distance (or changes of a distance or a position, i.e., a displacement) with an accuracy of better than an optical wavelength; for measuring the wavelength of a laser beam, or for analyzing a beam in terms of wavelength components; for monitoring slight changes in an optical wavelength or frequency (typically using the transmission curve of a Fabry-Pérot interferometer); for measuring rotations (with a Sagnac interferometer); for measuring slight deviations of an optical to surface from perfect flatness; for measuring the linewidth of a laser; for revealing refractive index variations or induced index changes in a transparent medium; for modulating the power or phase of a laser beam; for measurements of the chromatic dispersion of optical components; as an optical filter or for the characterization of ultrashort pulses via spectral interferometry. Depending on the application, the light source used with an interferometer can be very different.
Two main configurations of interferometers are generally used, based on the principles of a Mach-Zehnder interferometer and a Michelson interferometry. Mach-Zehnder interferometer determines a relative phase shift between two collimated beams from a coherent light source propagating along different paths towards a location where they interfere with one another, which phase shift is caused by a sample or a change in length of one of the paths. Michelson interferometer is a Mach-Zehnder interferometer that has been folded back upon itself. In the Michelson interferometer, the same beam splitting optics is used to recombine the beams.
Typically, interferometry is performed with two beams having the same polarization. Polarization-based interferometers, utilizing orthogonally polarized beams have been developed for various applications, e.g. distance and velocity measurements [3]. A Mach-Zehnder interferometer operating with radial polarization was demonstrated for the measurement of the geometric phase [1], and a radial polarizer was shown to be useful for a single shot birefringence measurement [2].